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Sustained nuclear localization of p21/WAF-1 upon growth arrest induced by contact inhibition
M G Ritt1, J Mayor, J Wojcieszyn
1Department of Small Animal Medicine and Surgery, Texas A&M University, College Station, TX 77843, USA.
Abstract:
We assessed the expression and distribution of p21/Waf-1 in TLM1 melanoma cells that exhibit contact inhibition and require serum for growth. The growth stage of cells stimulated to enter the mitotic cell cycle synchronously and grow to confluence was characterized by distinct, yet consistent levels and patterns of distribution of p21/Waf-1. Significantly, sustained accumulation of p21/Waf-1 in the nuclear compartment was seen only after 4 days in culture when cell-to-cell contacts were established, leading to a diminished rate of cell growth. Overexpression of wild-type waf-1 in melanoma cells reduced growth of subconfluent cells, decreased Cdk4 activity with a concomitant increase in hypophosphorylated Rb, and promoted cell death by apoptosis. The data support the premise that cell-to-cell contacts provide signals that mediate sustained nuclear localization of p21/Waf-1 leading to cell growth arrest; furthermore, an elevation in the activity of this protein can lead to apoptosis.
Insights
Cell-to-cell contact in melanoma cells signals sustained nuclear localization of p21/Waf-1, causing growth arrest. Increased p21/Waf-1 activity can also trigger apoptosis, impacting melanoma progression.
Area of Science:
- Cell biology
- Cancer research
- Molecular oncology
Background:
- Melanoma cell growth is regulated by various factors, including cell density and serum availability.
- p21/Waf-1 is a key cell cycle inhibitor implicated in growth arrest and apoptosis.
Purpose of the Study:
- To investigate the role of p21/Waf-1 expression and localization in TLM1 melanoma cells under conditions of contact inhibition.
- To determine how cell-to-cell contacts influence p21/Waf-1 activity and melanoma cell proliferation and survival.
Main Methods:
- Assessed p21/Waf-1 expression and distribution in TLM1 melanoma cells.
- Synchronized cells to study mitotic cell cycle progression and confluence.
- Overexpressed wild-type waf-1 in melanoma cells.
- Measured Cdk4 activity and retinoblastoma protein (Rb) phosphorylation status.
Main Results:
- Distinct p21/Waf-1 levels and patterns correlated with cell growth stages.
- Sustained nuclear accumulation of p21/Waf-1 occurred upon establishment of cell-to-cell contacts, coinciding with reduced growth.
- Overexpression of p21/Waf-1 reduced subconfluent cell growth, decreased Cdk4 activity, increased hypophosphorylated Rb, and induced apoptosis.
Conclusions:
- Cell-to-cell contacts signal for sustained nuclear p21/Waf-1 localization, leading to melanoma cell growth arrest.
- Elevated p21/Waf-1 activity can promote apoptosis in melanoma cells, suggesting a dual role in regulating cell fate.